Buffer device



Oct. 22, 1963 K. w. MAIER 3,107,906

BUFFER DEVICE Filed Jui 15, 1960 4 Sheets-Sheet 1 Fi l 1 N VEN TOR.

Karl W. Mui EI BY Maw.

0d. 22,1963 K. jw. Wm, v3 ;9

I r BUFFER m Filed July 15, 1960 Q4 Shets-Sheet 5 Eig Fig .15-

Fig.1 n INVENTW Kurl WMuiEr BY Maw Oct. 22, 1963 K. w. MAIER BUFFER DEVICE Filed July 15, 1960 4 Sheets-Sheet 4 Kle n- INVENTOR. KtLIl \AZ MELI E1 BY United States Patent Office Patented Get. 22, 1963 3,107,906 BUFFER DEVICE Karl W. Maier, 7 Cranberry Lane, Cheshire, Conn. Filed .iuly 15, B69, Ser'. No. 43,157 10 Claims. (Cl. 267-9) The present invention relates to buffer devices and is a continuation-in-part of my US. Patent No. 2,948,529, issued August 9, 1960.

In engineering there is often a need for special buffer devices which combine the usual spring property of receiving large amounts of mechanical energy at low maximum forces with the ability to permanently absorb a great amount of the received mechanical energy by conversion into heat via friction. The end buffer or the draft gear of a railway car, the suspension systems of automotive vehicles, or the recoil mechanisms of guns are examples of such applications.

These buffer devices are required to have a low rate of mechanical efliciency; that is, a low ratio of the mechanical energy returned to the mechanical energy received; or, in other words, a high damping. In recovery, the force of the buffer device is only a fraction of the force exerted during the compression stroke.

The usual types of springs, such as helical compression springs, are not well suited for this purpose: Although they delay the return of mechanical energy, there is only little absorption of energy and the return forces are almost as great as the compression forces. Therefore, in applications where high damping is required, these springs are to be supplemented by a special damping device.

For small mechanisms, a friction brake based on the principle of Coulomb friction is often chosen. For larger mechanisms, however, a hydraulic brake has certain advantages. The known types of friction brakes, among other limitations, have the disadvantage that they require rather accurate machining, resulting in relatively high cost and sensitivity in operation. The second group of hydraulic brakes, in addition, requires continuous maintenance and its force-deflection characteristics not only depend on the velocity of compression but also on the temperature, since the viscosity of the hydraulic fluid depends greatly on temperature.

Other known types of Coulomb friction brakes suffer from a great dispersion in brake force, as caused by variation of the coefficient of friction. In addition, they require considerable length and space.

The friction ring spring is one of the few mechanical bufler devices which combines spring properties with a pronounced ability to absorb mechanical energy permanently by converting it into frictional heat. This spring, which consists of a column of inner and outer rings with matching tapers, has considerably smaller forces during extension as compared with the compression stroke. The main applications are in the railroad field.

This spring type requires the use of high quality steel and an ideal surface roughness at the engaging taper surfaces. Furthermore, since the friction forces on the tapers have a marked influence on the function, the taper angle (a) can only be chosen Within a rather narrow range; that is, from 12 to 18, preferably 14. If the taper angle chosen is smaller than 14, the ring spring might not always recover its initial length but remains blocked. On

the other hand, if the angle chosen is larger than 14, then the entire spring assembly becomes too stiff and loses its value as a spring. In addition, the manufacture of a friction ring spring requires high accuracy in machining in order to guarantee proper alignment of the stacked ring elements during the operation. Furthermore, this spring column requires lubrication with a special grease in order to keep the friction conditions rather constant and to avoid the galling of the taper surfaces where high forces are being transmitted.

The invention in question clearly considers this situation and responds to the challenge to create a friction buffer device which does not have the above-described disadvantages. This difiicult problem was solved according to the invention by installing in the path of the moving mass and plunger a thereby influenced force transmitting unit, i.e., a recuperating spring, a closed air volume, a compressible fluid, etc., influenced by the displacement, velocity or acceleration of the moving mass, said force transmitting unit acting on a force-multiplying damping unit suitably arranged between the." plunger (mass) and the force transmitting unit and being also in contact with a friction surface on a stationary member. The stationary member contains also an end support, which bears against one end of the force transmitting unit.

The force-multiplying damping unit may consist of a brake seat, which in the axial direction is both flexible in itself and displaceable as a whole, and which is acted upon the recuperating spring and the plunger. This brake seat, by means of camming surfaces acting in outward or inward radial direction, is in contact with a both radially and axially displaceable intermediate element (brake shoe), which in turn contacts the axially extended riction surface of said stationary member, i.e., an outer housing or inner rod of preferably cylindrical shape. Under the influence of axial forces, the damping unit develops a tendency to expand and/ or contract in the radial direction.

The effect of the new damping buffer device can be increased at will within a wide range and in simple manner by the brake seat and the brake shoe, each containing several elements in axially flexible series arrangement, said elements cooperating by means of consecutive adjacent pairs of contact surfaces.

In practice, the new damping buffer device can be realized in simple form by the brake seat and the brake shoe consisting of coil springs, Where the coils of the same spring are spaced apart, but where the coils of both springs contact each other alternately. The brake shoe due to its helical shape is now designated as brake spring.

The angle (a) between the camming surface of the brake seat and the longitudinal axis of the buffer device is usually in the range of from 10 to However, if the need for definite recovery of the buffer device to its initial condition is more important than the desire for high friction forces, the camming angle will preferably be chosen to be 30 to 45 In such case, however, the resulting loss of damping friction force can again be compensated for by increasing the number (n) of coils of the brake spring.

This new damping friction buffer offers the special and unique advantage that the damping =(friction force) may be increased not only by the reduction of the eamming angle (on), which leads to the danger of self-jamming, but also by increasing the length of the brake spring greater number (n) of coils). This freedom in design permits the lowering of the mechanical rate of efiiciency of the buffer device to any desired amount without increasing the danger of self-jamming of the brake spring in extension. The well-known ring spring does not possess the latter design advantage and consequently is limited to a rather narrow range of damping rate.

The friction surface of the buffer device can be increased considerably by arranging the force transmitting unit such as the recuperating spring concentrically with and inside the force-multiplying damping unit influenced thereby. Here the recuperating spring is received telescopically in an axially displaceable cup which acts on the surrounding damping unit by means of an outer flange.

The invention can be realized in especially simple form by manufacturing the recuperating spring serving as forcetransmitting unit and the helical spring serving as the brake seat as one helical piece now designated as main spring.

Another way for inexpensive yet accurate manufacture is to machine only one of each pair of the adjacent force transmitting surfaces of the coils forming the brake seat or brake spring.

However, it is even simpler and cheaper to manufacture these elements of the damping unit from profile wire or profile bar stock of essentially triangular cross-section.

The attached drawings illustrate examples of the invention.

FIG. 1 is a longitudinal section showing the basic arrangement of the buffer device;

FIG. 2 is a force-deflection diagram for the buffer device shown in FIG. 1;

FIG. 3 is a sectional view similar to FIG. 1 but showing a bulfer device in which the brake seat is internally in contact with a stationary rod;

FIG. 4 is a section of one of the coils of the brake seat shown in FIG. 3;

FIG. 5 is a view similar to FIG. 3 but showing a buffer device in which the recuperating spring and the brake seat are formed as a single unit;

FIG. 6 is a view similar to FIG. 3 but showing a buffer device in which the brake seat is internally supported by an extension of the plunger;

FIG. 7 is a view similar to FIG. 5 but showing a buffer device in which the outer housing has been eliminated leaving only one friction surface;

} FIG. 8 is a sectional view of a buffer device in which the brake seat surrounds one end of the recupterating spring to reduce the overall length of the device;

FIG. 9 is a view of the buffer device shown in FIG. 8 after full compression by the plunger;

FIG. 10 is a fragmentary sectional view of the damping unit portion of FIG. 3 but showing the coils of the outer or brake spring divided longitudinally into sections;

FIG. 11 is a longitudinal section of a bufier device in which the housing is flexible in the radial direction;

FIG. 12 is a longitudinal section of a buffer device similar to those shown in FIGS. 3 and 5 but designed to act in tension; and

FIG. 13 is a reduced side view of a section of a buffer chain made from a number of the buffer devices of FIG. 12 and showing one of them in longitudinal section.

FIG. 1 shows the force multiplying eifect of the new damping friction buffer in a fundamental manner. A stationary tubular housing G contains a recuperating spring R, a damping or friction unit D, and a moving mass or plunger M which is to be bufiered. The inner wall of the housing G serves as friction surface for the friction unit D. The recuperating spring R acts with a force P according to its deflection. P designates the force acting on the moving mass M. On the other hand, the damping unit D receives axial end forces P I and-as a result of its P =C.P P 51 since C 1 M (extension stroke)-Now the recuperating spring is the source of energy:

In FIG. 2 a forcedeflection diagram of the new damp ing friction buifer is shown which gives the comparison of the buffer forces during the extension stroke, P as compared to the compression stroke, P for a damping unit of one and (n) elements.

FIG. 3 illustrates an example of a new friction bulfer by means of a longitudinal section. A cylindrical rod 2 and a cylindrical housing 3 surrounding the latter with equal radial spacing are fastened to a stationary member 1 by means of threads 4 and 5. Between the two parts 2 and 3, a force transmitting unit in the form of a recuperating spring 6 is installed and adjacent to it, a disc 7 and a couple of nested springs 8 and 9 in concentric arrangement, where the coils of the inner spring 8 lie be tween the coils of the outer spring 9, and where the coils of the same spring do not contact each other. Springs 8 and 9 function as brake seat and brake spring, respec-* tively.

The contact surfaces 10 and 11 of these two springs 8 and 9 on the rod 2 or the outer housing 3, respectively. are peripherally formed to fit the corresponding cylindri cal contact surfaces 12 and 13 of rod and outer housing.

Furthermore, the outer surface of inner spring 8 is also ground under an angle (on), which is 45 in the example shown. The surfaces 14 and 15 so obtained (FIG. 4) are in contact with the adjacent coils of the outer spring 9.

The inner spring 8 is acted upon by the disc 7 and also by the axially movable plunger 16, which is in contact with the striking mass. The outer spring 9, in general, has neither contact with the disc 7 nor with the plunger 16.

The force P of the recuperating spring 6 causes axial forces to be transmitted through the buffer device as indicated by the arrows P and P in FIG. 3. The force of the recuperating spring is transmitted forward to the adjacent coil of the inner spring 8 and is divided there essentially into two components, one in the radial direction and the other perpendicular to the camming surface. The latter force is transmitted to the adjacent coil of the outer spring 9 and is again divided into two component forces, first a normal expansion force with resulting tangential friction force on the inner wall of the housing and a second force perpendicular to the camming surface of the next following coil of the inner spring 8. From the equilibrium of the three forces acting on a coil element of the outer spring 9, it is concluded that the force transmitted to the camming surface of the following coil of inner spring 8 is greater than the force received from the carnming surface of the preceding coil of inner spring 8.

Likewise, the forces are transmitted through the fol- The above discussion shows that a force transmitted through this new friction buffer device can be efficiently damped within a small length or volume, whereby the desired rate of damping can be very closely controlled over a rather wide range by selection of the taper angle (a) and the number (n) of the coils generating the friction forces.

The design version of FIG. 5 is fundamentally the same as the above-discussed design of FIG. 3. However, here the recuperating spring and the inner spring of the damping unit are made from one piece 19 where the latter is provided with outward camming surfaces 14, 15, in the region of the outer spring 9 only. Spring 19 is the main spring of the buffer device.

FIG. 6 is similar in structure to FIG. 3, but the stationary inner rod is eliminated, so that the friction force 18 occurs only at the outer housing 3. FIG. 6 also shows a plunger 16 with an extension rod 161 which reaches inside inner spring 8 and, of course, moves axially with the plunger 16. If this inner rod 161 has considerable radial clearance inside the spring 8, it can never contact the latter over its entire circumference, but still can serve as a guide for the plunger 16. With small radial clearance, however, the part 161 may serve as an inner support for the brake seat spring 8 to permit the transmission of higher forces.

FIG. 7 illustrates another design configuration where the outer housing is eliminated so that the friction force 17 occurs only at the inner rod 2.

While with the above-described design versions, the recuperating spring and the damping unit are arranged in space one after the other, FIGS. 8 and 9 demonstrate the possibility of arranging one concentrically inside the other, in telescopic fashion. The two figures show the damping bulfer device in the status of maximum and minimum length, thus demonstrating the compactness of this design. Here the recuperating spring 6 is received telescopically in an axially displaceable cup 2% (taking the place of the above-described disc 7), which by means of an outer flange 21 acts on the inner spring of the surrounding damping unit (3; 8, 9).

FIG. 10 illustrates a buffer spring construction similar to that shown in FIG. 5 but where coils 9 are in the form of separate sections which are each split as shown at 22 to respond to the camming action of the corresponding coils of main spring 19.

The relatively displaceable and friction generating component parts of the new friction buffer device are preferably made from metals of various types and proper hardness; for example, an outer housing made from steel may receive an outer spring 9 made from Phosphor bronze. In other cases, the housing may also have an inner liner of automotive brake material.

In the configurations described above, or similar ones, the housing 3 serves as a support for the radial expansion forces of the damping unit and also as a friction surface. In order to perform this function, it may be thickwalled and therefore rigid. However, the housing may also be rather flexible in the radial direction and may expand in that direction by several percent during the compression stroke of the buffer. Within certain limits, the zig-zag type force transmission characteristic for the new buffer device and the multiplied braking effect resulting therefrom is not altered by the housings radial expansion. However, such housing with radial flexibility makes possible the storage of additional energy by acting as expansion spring. FIG. 11 illustrates such a design version, where housing 3 is formed by a longitudinally split and therefore highly expandable inner steel liner 23 surrounded by a sleeve 24 made from highly elastic material.

The design versions discussed above demonstrate the use of the new device for the damping of compressive forces and impacts. However, the buffer device can be equally well applied to the absorption of tension forces and to the damping of tensional impacts. FIG. 12 illustrates a corresponding design modification by means of a single buffer element. In FIG. 13 a highly damping buffer chain composed of such single bulfer elements is shown.

What is claimed is:

1. A buffer device comprising a member having a friction surface and an endsupport, a helical main spring being at one end in contact with said end support and having a plurality of interspaced coils, a slideable plunger disposed in contact with the other end of said main spring for reciprocal movement therewith along an axis parallel to said friction surface, and a helical brake spring having a plurality of interspaced coils disposed in alternate nested relation with said coil-s of said main spring at the end adjacent said plunger whereby said brake spring coils are radially expanded into contact with said friction surface in response to the axial movements of said main spring coils during the reciprocal movement of said plunger.

2. The combination defined in claim 1 wherein said friction surface is formed by the inner wall of a cylindrical housing surrounding-the combination of said main and brake springs.

3. The combination defined in claim 1 wherein said friction surface is formed by the exterior surface of a cylindrical rod fixedly secured to said end support to extend longitudinally through said main spring coils for supporting contact with said plunger.

4. The combination defined in claim 1 wherein said friction surface is formed by the inner wall of a cylindrical housing surrounding the combination of said main and brake springs and a second friction surface is formed by the exterior surface of a cylindrical rod fixedly secured to said end support to extend longitudinally through said main spring coils for supporting contact with said plunger.

5. The combination defined in claim 1 wherein said helical brake spring is subdivided lengthwise into sections.

6. The combination defined in claim 1 wherein said plunger is provided with an extension of smaller diameter passing through said main spring coils for imparting radial support thereto.

7. A buffer device comprising a cylindrical housing having a closed end and a friction surface along the inner wall, a slideable plunger extending into the opposite end of said housing for axial reciprocation therein, a helical main spring seated between said plunger and said closed end of said housing, said main spring having a first series of interspaced coils with a circular cross-section disposed adjacent said closed end of said housing and a second series of interspaced coils with a nearly triangular crosssection disposed adjacent said plunger, and a helical brake spring having a plurality of interspaced coils disposed in alternate nested relation with said second series of said main spring coils, said brake spring coils having a cylindrical surface on the exterior for mating engagement with said friction surface in said housing whereby axial displacement of said main spring in either direction cams said brake spring coils into frictional engagement with said friction surface on said housing to modify the forces acting on said plunger.

8. The combination defined in claim 7, wherein said triangular exterior of said second series of said main spring coils forms camming angles with respect to the axis of the buffer device ranging from 10 to 70.

9. The combination defined in claim 7 wherein said housing is divided into an inner liner of steel having a plurality of longitudinal splits about the circumference and an outer sleeve of a highly elastic material whereby the resulting radial flexibility of said housing assists the main spring in absorbing energy from the plunger.

10. A buffer device comprising a cylindrical housing having a closed end and a friction surface along the inner wall, a slideable plunger extending into the opposite end of said housing for axial reciprocation therein, a helical main spring seated between said plunger and said closed end of said housing, said main spring having interspaced coils of circular cross-section, and a helical brake spring having a plurality of interspaced coils disposed in alterhate nested relation with the coils of said main spring at the end adjacent said plunger, said brake spring coiis having a cylindrical surface on the exterior for mating engagement with said friction surface in said housing and having two surfaces of constant inclination to the axis of said cylindrical housing for engagement with said main spring coils, whereby axial displacement of said main spring in either direction cams said brake spring coils into frictional engagement With said friction surface on said housing to modify the forces acting on said plunger.

References Cited in the file of this patent UNITED STATES PATENTS Brooks May 16, 1916 Gross Feb. 18, 1930 Sproul June 28, 1938 Holland Dec. 12, 1939 Maier Aug. 9, 1960 FOREIGN PATENTS Germany Feb. 21, 1928 Belgium June 1, 1950. 

1. A BUFFER DEVICE COMPRISING A MEMBER HAVING A FRICTION SURFACE AND AN END SUPPORT, A HELICAL MAIN SPRING BEING AT ONE END IN CONTRACT WITH SAID END SUPPORT AND HAVING A PLURALITY OF INTERSPACED COILS, A SLIDEABLE PLUNGER DISPOSED IN CONTACT WITH THE OTHER END OF SAID MAIN SPRING FOR RECIPROCAL MOVEMENT THEREWITH ALONG AN AXIS PARALLEL TO SAID FRICTION SURFACE, AND A HELICAL BRAKE SPRING HAVING A PLURALITY OF INTERSPACED COILS DISPOSED IN ALTERNATE NESTED RELATION WITH SAID COILS OF SAID MAIN SPRING AT THE END ADJACENT SAID PLUNGER WHEREBY SAID BRAKE SPRING COILS ARE RADIALLY EXPANDED INTO CONTACT WITH SAID FRICTION SURFACE IN RESPONSE TO THE AXIAL MOVEMENTS OF SAID MAIN SPRING COILS DURING THE RECIPROCAL MOVEMENT OF SAID PLUNGER. 